Method for increasing the thrust of jet engines by the use of rapidly decomposable nitrogen compounds



G. N. CADE 2,636,342

THE THRUST OF JET ENGINES BY ECOMPOSABLE NITROGEN COMPOUNDS Filed Jan. 4. 1949 (NITROGEN COMPOUND April 28, 1953 METHOD FOR INCREASING THE USE OF RAPIDLY D W IIII VIIkH EXHAUST NPZZLE/IQ NITROGEN COMPOUND TURBINE HOLDER 23 ?\FLAME HOLDER IN V EN TOR.

(FLAME FUEL.

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FUEL

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coMPREssoR NITROGEN COMPOUND) G. N. CADE BY 2 p ATTORNEYS Patented Apr. 28, 1953 METHOD FOR INCREASING THE THRUST OF JET ENGINES BY THE USE OF RAPIDLY DECOMPOSABLE NITROGEN COMPOUNDS George N. Cade, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application January 4, 1949, Serial No. 69,247

(01. Gil-35.4)

6 Claims.

This invention relates to jet engines. In one of its more specific aspects it relates to the operation of jet engines. In another of its more specific aspects it relates to a method for intermittently and continuously operating jet engines.

Jet engines, which may be generally classified as aerodynamic power plants, fall specifically into three distinct categories, i. e., ram jets, turbo jets and pulse jets. The working cycle of the ram jet and the turbo jet is essentially the same. One distinct difference in operation, however, is apparent in the compression step. Air is jammed into the combustion zone of the turbo jet by a gas turbine. Compression in a ram jet engine is provided by the ramming effect of the oncoming air. Compression in the pulse jet engine is obtained by oncoming air and by the intermittent closure of valves upstream of the combustion zone to prevent the escape of gases through the upstream end of the engine.

Fuel which is injected into the combustion zone of the above designated jet engine may originally be ignited therein by a spark producing device, such as a conventional spark plug mounted in the wall of the combustion chamber. Additional fuel is thereafter ignited by the flame of burning fuel or by the heat from hot combustion gases remaining in the combustion zone or by heat from the hot combustion chamber wall. The air and exhaust gases within the combustion zone are heated by the heat of combustion and are exhausted from the combustion zone through a rearwardly extending exhaust conduit at an exit velocity higher than the flying speed of the engine. The thrust produced thereby equals the gas mass flowing through the exhaust duct times its increase in speed, according to the law of momentum.

Attempts are now being made to develop jet powered air craft that will operate at very high altitudes and at sonic or supersonic speeds. Such jet engines require the use of fuels which will produce a maximum of power per unit liquid fuel volume. Generally speaking, those hydrocarbon fuels which will produce the greatest temperature rise through the jet engine have proved to be highly desirable for producing the greatest amount of thrust.

Other factors which must be considered in connection with the selection of a fuel for ram jet, turbo jet, and pulse jet engines are the ignition and combustion speed of the fuel. These fuel qualities are particularly important in connection with the operation of the ram jet and turbo jet engines. In the latter two engines a peculiar operational problem is encountered which is not generally found in the operation of a pulse jet engine. As air flow through the ram and turbo jet engine increases, the flame front is carried further and further to the rear of the combustion chamber. In some cases the flame front has a tendency to move downstream from the fuel injection nozzles in the engine, and then to return to a point adjacent the nozzle tips and to periodically follow the same combustion pattern. That type of combustion pattern is known as cycling. A characteristic noise is produced when the fuel burns in this manner and the flame is often near the point of blow out. Blow out is the point at which the flame is completely extinguished as it moves further and further away from the fuel injection nozzle tips.

Figure 1 diagrammatically sets forth a pulse jet engine. Figure 2 diagrammatically shows a turbo-jet engine. Figure 3 diagrammatically shows a ram-jet engine.

An object of this invention is to provide an improved method for operating jet engines. Another object of this invention is to provide an improved method for increasing the thrust of jet engines. Another object of this invention is to provide improved means for increasing the thrust of jet engines even with ordinary hydrocarbon fuels. Another object of this invention is to provide a method for extending the operational limits of jet engines. Another object of the invention is to reduce cycling in a continuous combustion jet engine. Other and further objects and advantages of the invention will be apparent upon study of the accompanying disclosure.

Generally speaking, the invention resides in the injection into the combustion zone of a jet engine of a normally nongaseous nitrogen compound which decomposes rapidly upon heating to give large volumes of gas. The nitrogen compound may be injected into the combustion chamber in the form of a comminuted solid. It may also be suspended in a gas, such as nitrogen, and injected into the combustion zone as a suspension. One preferred method of injecting the nitrogen compound into the combustion zone is to form a solution of the nitrogen compound in alcohol and to inject the solution into the combustion zone as a spray. Other solvents, such as water, may also be used, although a Water solvent has a relatively high freezing point and in many types of operation would not be a desirable means for injecting a nitrogen compound into the jet engine combustion zone. Normally solid nitrogen compounds decompose rapidly upon heating and give a large volume of gas. Among the preferred nitrogen compounds which may be utilized in this prises an elongated shell [2 open at its upstream and downstream ends so as-to permit'thepassageof air therethrough. Immediately'downstream of the upstream end of engineill is"a plurality -ofi flapper valves 13 which open in response to normal flow of air through engine'l i butwhichcldse upon the pressure downstream oi'th'evalves-be coming greater than the pressure of the incoming air. diately downstream of valves l3, and nitrogen compound inlet conduitsv l and I6 havingvalves therein are provided downstream of valves I3, inlet I5 preferably being upstreamof i'uelinlet conduit l t-and conduit 1 6* being downstreamv of the fuel inlet corrduit. Flame-h'oldenil which may be of any conventional type of name holder, is provided downstream of the fuel inlet conduit and preferably-upstream of 'in'let conduit I6; A combustion zone l8-' is' formed downstream of flame holder ll' wherein fuel; generallya hydrocarbon fuel, is burned in the presenceot air, and a nitrogen compound'introduced through atleast one of the inlet-conduits"! Band l Sis decomposed therein. Gasesresulting from theburned hydrocarbonand decomposed nitrogen compound are exhausted through anexhaust-zone 'l 9 in the downstream end of engine 1 I;

Figure 2- is adiagrammatic representation of a turbojet engine: Parts like" those described" in connection with *Fi'gure--'1-of the-drawing are indicated'by' likenumerals; Turbojet engine 2 comprises an elongated shell-22 open at its upstream and downstream ends'so as-to permit high velocity gases'to flowtherethrough; Turbine23 is provided downstream 1 of combustion 7 zone l8 and the gases resultingfrom the burning and decomposition of hydrocarbon fuel and nitrogen compound within-the combustion zone are expanded through" turbine 2 3" to the atmosphere through the exhaust zone [9; Turbine 2 3- is operatively connectedto-compressor 24 which is positioned upstream" of c the fuel and nitrogen compound inlet conduits." compressoivm'aids'in compressing. the high velocity air stream supplied to the combustion. zone.

A ram'jet engineis "diagrammaticallyshownin Figure 3 of theorawing: Rama-jet; engine 25.

comprises an elongatedshell' 2B; open'at itsupstream and downstream ends soast'o permit the flow of high velocitygastherethrough. The fuel inlet I4 and nitrogen 1 compound inlets l5" and I6 together with flameholder' l! are positioned similarly to that shown in connection with Figures 1' and'2. Combustion zone l8' and exhaust zone I!) are also similar tothose' showniin' connectionwith Figures 1" and 2l'of the drawing.

As pointedlout above, the thrust produced? by a jet engine equals .the mass. flow through the exhaust duct times: itsincrease in speed; By producing larger volumes of 'gasf'in the combustion zone by. meansoi'thisinvention,- a substantially greater gasvmass is-causedto now through:

Fuel inlet conduit Wis-provided imme jet engine at operational efliciency. When too much of the nitrogen compound is injected into the combustion zone of the jet engine, a back pressure is produced which tends to cut down on the 'operatlo'nal eflioiency of theengine. The jet engines should beoperated so that the gas liberated by the decomposition of the nitrogen compound is less than the volume of other gases in thecombustion chamber. Generally speaking, the-ratio of gas produced by the decompositionof nitrogencompound to other gases in a jet engine combustion chamber should be maintamed-within the-limits of from 121.25 to 1:10. Itisprefrred, however, to maintain the ratio within the'limitsbf from 1:2 to 1:5.

Thepoint at which the normally solid nitrogen compound is injected into the combustion zone of af'jet engine should be carefully selected so as to insure proper heating of the nitrogen compounda Although' the nitrogenv compound is decomposed iii it 1 is:: injected at a point upstream of the fuel injectionipoint; best operati'on 1s obtained when the 1 material is injected into the combustiorr zonefat a" point downstream ofthe fuel injection pointi In ram jet and turbo jet engines the combustion zone may' comprise nearlythe entirestructure downstream from the fuel =inj ectiom- The" above designated jet: engine types may generally' be operated by injecting a hydrocarbon fuel an'd' air into the combustion zone' of the j et engine'- at a fuel airratio between .005 and .10 andigniting the fuel so as to heat the air and combustion gases; thus increasing the volume of gas mass which is exhausted through the exhaust zone-of?thejet engine;. Turbo .jet engines arepreferably operated on=a fuel-air ratio between-.01 andi03'3 Ram jet and pulse jet engines are preferably operated at fuel-air ratios of from .(l3 to'n07i Ifr'theoperation of this invention fuel and aii' are: injected into the combustion zone" of -'the engine at a fuel-air ratio between .005'and .10. At least Eonenormally solid nitrogen compound is ir'ijected into said combustion zone at sucha rate=that upon-decomposition of the nitrogen comp'ound the ratio of the gas produced thereby to the other gases in-the combustion chamber is withifithe range of from 1 1.25 "to 1:10. The fuel is-burned in thecombustion zone so as to heat the-air andcombustion' gases and at the same time decompose the nitrogen compound. The-gasma'ss is thenexhausted from the combustion zone" through a rearwardly extending exhaustzone; thereby'increasing the speed of the engine" by, the increased" thrust of the exhaust gases "in the'exhaust' zone;-

This invention not only. results in'anincrease in the thrust .of a'jet' engine, but'also'tends to obviateicycling "and" also extends the operational "limits ofi'jet englnes-byi'increasing the speed of the engine beforeblowoufipointis reached. It is believed'lthat theresult in reducing cycling and the'tendenoy'to extend theoperational limits of th'ejet I engineiis'. due to' the increased compression which"is ma'ddp'ossible by the increased volume of gas -presentinthe combustion zone. .By. utilizing, this invention a hydrocarbon fuel having; poorercombu'stion' characteristics than are ordinarily. desired"mayfbe utilized and will produce betterl'results than had been obtained with them heretofore:

Asanxexample of 'howlth'isiinvention operates, itl shouldbe; noted. that grams (47cc) of ammonium nitrate'decomposesltmgive 67 liters of'gas' at"standardtemperature and pressure.

If, however, the temperature is raised to about 1650 C. at atmospheric pressure, which is within the temperature range of a ram jet exhaust gas, the volume of resulting gases is about 470 liters. The gas mass which is thus made available for exhaust is substantially increased thereby.

Other modifications will be apparent to those skilled in the art upon study of the accompanying disclosure. The principle of this invention may be utilized to increase the power output of nonaerial gas turbine power plants. This modification together with other obvious modifications is believed to be within the spirit and scope of the disclosure.

I claim:

1. In a method for operating a jet engine in the propulsion of an aircraft, wherein high velocity gas passes successively through a compression zone, a combustion zone, and an exhaust zone at operating conditions of varying severity such as result in unstable burning of fuel in said combustion zone and wherein hydrocarbon fuel and air are injected into said combustion zone of said jet engine at a fuel-air ratio between .005 and .10; the improvement which comprises injecting into said combustion zone a normally solid nitrogen compound selected from the group consisting of ammonium nitrate, ammonium nitrite, hydroxylamine nitrate, urea, and urea nitrate, at such a rate that the ratio of gas produced from said nitrogen compound to other gases in said combustion zone ranges from 1:2 to 1:5; burning said fuel with said air in said combustion zone so as to heat any excess air and combustion gases and decompose said nitrogen compound to form a gas in such quantity as to stabilize the burning of said fuel; and exhausting said gases from said combustion zone through an exhaust zone.

2. A method of claim 1, wherein said nitrogen compound is urea; and the ratio of gas produced from said injected nitrogen compound to other gases in said combustion zone ranges from 1:2 to 1:5.

3. A method of claim 1, wherein said nitrogen compound is urea nitrate; and the ratio of gas produced from said injected nitrogen compound to other gases in said combustion zone ranges from 1:2 to 1:5.

4. The method of claim 1, wherein said nitrogen compound is ammonium nitrate; and the ratio of gas produced from said injected nitrogen compound to other gases in said combustion zone ranges from 1:2 to 1:5.

5. The method of claim 1, wherein said nitrogen compound is ammonium nitrite; and the ratio of gas produced from said injected nitrogen compound to other gases in said combustion zone ranges from 1:2 to 1:5.

6. The method of claim 1, wherein said nitrogen compound is hydroxylamine nitrate; and the ratio of gas produced from said injected nitrogen compound to other gases in said combustion zone ranges from 1:2 to 1:5.

GEORGE N. CADE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,393,594 Davis Jan. 29, 1946 FOREIGN PATENTS Number Country Date 574 Great Britain Feb. 1'7, 1875 15,852 Great Britain Aug. 2, 1905 154,254 Great Britain Nov. 22, 1920 459,924 Great Britain Jan. 18, 1937 

1. IN A METHOD FOR OPERATING A JET ENGIN IN THE PROPULSION OF AN AIRCRAFT, WHEREIN HIGH VELOCITY GAS PASSES SUCCESSIVELY THROUGH A COMPRESSION ZONE, A COMBUSTION ZONE, AND AN EXHAUST ZONE AT OPERATING CONDITIONS OF VARYING SEVERITY SUCH AS RESULT IN UNSTABLE BURNING OF FUEL IN SAID COMBUSTION ZONE AND WHEREIN HYDROCARBON FUEL AND AIR ARE INJECTED INTO SAID COMBUSTION ZONE OF SAID JET ENGINE AT A FUEL-AIR RATION BETWEEN .005 AND .10; THE IMPROVEMENT WHICH COMPRISES INJECTING INTO SAID COMBUSTION ZONE A NORMALLY SOLID NITROGEN COMPOUND SELECTED FROM THE GROUP CONSISTING OF AMMONIUM NITRATE, AMMONIUM NITRITE, HYDROXYLAMINE NITRATE, UREA, AND UREA NITRATE, AT SUCH A RATE THAT THE RATIO OF GAS PRODUCED FROM SAID NITROGEN COMPOUND TO OTHER GASES IN SAID COMBUSTION ZONE RANGES FROM 1:2 TO 1:5; BURNING SAID FUEL WITH SAID AIR IN SAID COMBUSTION ZONE SO AS TO HEAT ANY EXCESS AIR AND COMBUSTION GASES AND DECOMPOSE SAID NITROGEN COMPOUND TO FORM A GAS IN SUCH QUANTITY AS TO STABILIZE THE BURNING OF SAID FUEL; AND EXHAUSTING SAID GASES FROM SAID COMBUSTION ZONE THROUGH AN EXHAUST ZONE. 